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Airborne mapping technologies help manage forest resources

Edith Chenault | Apr 13, 2004

Through the red eye of an airplane-borne scanning laser, individual trees emerge distinct from thickets, and the undergrowth beneath the tree canopy appears as if by magic. Take a plane ride with Sorin Popescu, and you’ll see Texas forests in a new way. The scientist is researching how accurate and effective LIDAR remote sensing is in assessing the potential for forest fire in the state.

LIDAR – an acronym for Light Detection and Ranging – uses laser light to measure the distance from an airborne sensor to a reflective surface on the ground, says Popescu, assistant professor with Texas A&M University’s Spatial Sciences Laboratory and department of forest science. Covering the ground with 70,000 laser pulses per second, LIDAR can collect three-dimensional data about the earth’s surface in amazing detail.

The Texas Forest Service is interested in LIDAR because it holds the promise to more easily and accurately determine how much and what kind of dead vegetative material -- potential fuel for wildfires – exists in forests and brushy areas. The greater the buildup of these fuels, the higher the risk of fire danger.

Satellite imagery and aerial photography are currently used to make these assessments, but these technologies do not accurately measure the amount of fuel present, especially under forest canopies.

“Since LIDAR is able to penetrate the canopy and provide a three-dimensional perspective, our hope is that it will provide us with the additional information we need,” says Curt Stripling, geographic information systems coordinator for the Forest Service, who is working on the project with Popescu.

Tom Spencer, the agency’s risk assessment coordinator, says, “It is important for us to accurately determine fuel types, particularly in the high-risk areas of the state where people are in close proximity to wild land fuels. We call this the Wild land-Urban Interface. Many of the state’s 20 million residents make their homes in this interface zone. Being able to better determine the fuel types will increase our accuracy in defining where these high-risk areas are.”

The LIDAR sensor will be flown over a 35-square-mile test area in Walker County. Scientists will compare the data taken from the air with that gathered from ground sample plots.

“We will take the information and determine whether it answers the question we initially asked: Will it provide us a more detailed perspective of fuels in an area, and will it add to our understanding of the wild land fire risk?” Stripling says.

LIDAR mapping is just one way the Spatial Sciences Laboratory is helping people see the world in new ways. The lab offers a range of services, from providing information for natural resource managers across the state, to mapping the boundaries of lakes managed by the U.S. Army Corps of Engineers, to training the next generation of students in spatial sciences.

Raghavan Srinivasan, director, says the lab downloads and creates data from many sources, including satellites owned by the federal government. The satellites are 400 to 500 miles aloft, but some are so accurate, “every 2 feet is imaged,” Srinivasan says. “You can pretty well pick out a car or a truck on the road and sometimes tell what the model is.”

The spatial sciences divide into three categories:

-- Global positioning systems, which use an array of satellites and can provide the exact location of anything on the earth at any time;

-- Remote sensing, which can include any device capable of gathering information about a distant object; and

-- Geographic information systems, which can be any software capable of analyzing the sensed data and its locations.

One of the lab’s most popular products is the Soil and Water Assessment Tool, the first and most widely used of its kind in the world. Using GIS software and maps and data collected from the field, the SWAT computer model is used to predict effects of non- point source pollution on watersheds. The idea was conceived in the 1990s by Jeff Arnold, agricultural engineer with the USDA Agricultural Research Service in Temple, and Srinivasan, who was then with the Texas Agricultural Experiment Station Blackland Research Center in Temple.

Researchers needed to know what effects management decisions had on water, sediment, nutrients and pesticides in watersheds and river basins across the nation, Arnold says. But computer models then in use predicted conditions limited to areas were the size of crop fields.

In the early 1990s, Arnold began expanding the areas the models could cover, until, “we ran the SWAT model across the United States,” he says.

Weather, soil and topographical information from satellite maps and fieldwork feed into the model, which contains equations that estimate what could happen under different circumstances.

Agencies such as the U.S. Environmental Protection Agency and the Texas Commission on Environmental Quality use SWAT to assess water quality and pollution risks to surface and groundwater. Other scientists have used the model to predict the effects of climate change on water supplies.

Use of SWAT has now spread to Europe and Asia, and it has become “one of the most widely used watershed models in the world,” says Allan Jones, director of the Texas Water Resources Institute. Srinivasan and Arnold have provided SWAT modelers to more than 100 countries.

Because of their expertise, Srinivasan and Arnold have trained professionals from all over the world. Representatives from 55 countries have attended the international workshops held every other year. Martin Volk, who attended the first international SWAT workshop in Giessen, Germany, is now working at the Grassland Soil and Research Lab in Temple helping to expand the model’s capabilities even further.

Volk, a working group leader at the Center for Environmental Research in Leipzig, Germany, says SWAT is used in his country to help farmers determine the impact of organic crops on water and land resources. It also helps governmental agencies recommend how best to manage land subject to erosion.

He says SWAT’s strength is its ability to analyze and assess large areas of land and to integrate nutrients and the water cycle into the equations.

“It’s good to have one tool,” Volk says, adding that other models often separate the components.

The lab is increasing the number of students trained in spatial sciences here at home as well. The number of undergraduate students enrolled in spatial sciences classes at Texas A&M has increased from 35 to 90 and the number of graduate students from 10 to 24 in the past several years. The lab offers master’s and doctoral programs through the departments of forest science and biological and agricultural engineering.

The College of Agriculture and Life Sciences and the College of Geosciences have recently agreed to offer an undergraduate degree in spatial sciences starting Fall 2004, Srinivasan says.

Professionals who want to add skills also can take part in the continuing education programs offered by the lab.